This invention relates to heat exchangers and more particularly to an improved radial flow heat exchanger in which the fluid to be heated or cooled flows between an outer peripheral portion of the heat exchanger, through a plurality of radially extending tubes, and a center hub, the tubes passing through a fin arrangement.
Various types of heat exchangers are known such as shell in tube heat exchangers and radial flow heat exchangers. In the radial flow heat exchangers of the prior art, fluid flow tubes are arranged in a helical manner with the flow of fluid being in a spiral fashion through the helically formed tubes. Typical of the prior art patents related to radial flow heat exchangers are the following: Kissinger, U.S. Pat. No. 4,182,413 of 1980; Gilli et al, U.S. Pat. No. 3,712,370 of 1973; Tipman et al, U.S. Pat. No. 5,088,550 of 1992; Borjesson et al. U.S. Pat. No. 4,128,125 of 1978; Dobbins et al, U.S. Pat. No. 4,883,117 of 1989, by way of example.
In addition to the above, there are numerous patents dealing with heat exchangers such as those with radial baffles, U.S. Pat. No. 4,642,149; spiral heat exchangers, U.S. Pat. No. 4,993,487; circumferential flow heat exchangers, U.S. Pat. No. 5,343,936; finned tube heat exchangers, U.S. Pat. No. 5,355,944, as an example.
While most of the prior art heat exchangers generally operate satisfactorily for their intended purpose, in some cases, the heat exchanger is of a complex shape, relatively expensive to manufacture, sometimes have a relatively large profile and has an efficiency less than that desired.
Thus, there is a need for an improved radial flow heat exchanger which is relatively easy to manufacture, of a relatively small profile and which operates efficiently.
An object of this invention is to provide an improved radial flow heat exchanger in which fluid flows from a manifold which includes a plurality of radially spaced flow tubes, connected at their other end to an exit manifold.
Another object of this invention is to provide a radial flow heat exchanger in which a cooling or heating fin structure is positioned in heat conducting contact with radially arranged tubes which pass through apertures in the fin structure.
Yet another object of this invention is the provision of an improved, relatively simple radial heat exchanger which is compact in profile and which is relatively easy to manufacture and assemble.
These and other objects are achieved in accordance with this invention by a unique design of a heat exchanger that is preferably round in shape (or other shape) and which radially directs the fluid to be heated or cooled between the outer perimeter of the heat exchanger and the center of the circle (hub) through several radially disposed tubes (spokes) which interconnect the hub to the perimeter ring. As the fluid travels towards or away from the center, heat is exchanged via a wound spiral ribbon of heat exchange material (fins), such as aluminum sheet metal, through which the tubes pass. When the fluid gets to the exit of the exchanger it is collected and directed back to the component from which heat is being extracted (or to which it is being added).
In a preferred form, the fluid to be cooled or heated enters into the hollow outer ring through a fluid inlet. The fluid then flows around the perimeter of the hollow outer ring and through all the hollow fluid carrying xe2x80x9cspokesxe2x80x9d. As the fluid passes through the spokes it gives off or picks up heat conducted through the fins. One could use a fan to force air through the fins, or one could use the heat exchanger without a fan at all. Even without forced convection, the radial heat exchanger concept has inherent benefits over a traditional, folded-fin heat exchanger. It is understood however, that the fluid flow may be from the hub to the outer ring, again in a radial direction. Following are some of the benefits over a conventional heat exchanger.
(1) Packagingxe2x80x94If forced convection is used (a fan), and if the fan is approximately the same diameter as the radial heat exchanger, the need for a transition duct to direct the air flow evenly over all the fins is not necessary, as it would be if using a fan to cool a rectangular shaped exchanger efficiently. This elimination of the transition duct reduces the package thickness. Although some rectangular heat exchangers are cooled by fans without using a transition duct, the result is an inefficient use of material.
(2) Ability to be Optimizedxe2x80x94When the fluid enters the outer ring (a preferred form) it has the most heat (or ability to absorb heat) at this point. Using the equation for convective heat transfer, as set forth below, it can be shown that the heat transfer can be optimized with a radial design.
Q=h*A*(T1-T2) where:
Q is the convective heat transfer,
h is the convective heat transfer coefficient,
A is the surface area of the fins,
T1 is the temperature of the air flowing over the fins, and
T2 is the temperature of the surface of the fins
The various realities of the equation above include:
(a) The greater the fin surface area, A, the greater the convective heat transfer, Q.
(b) The greater the convective heat transfer coefficient, h, the greater the convective heat transfer, Q.
In other words, heat transfer will increase as the fin surface area and the heat transfer coefficient increase. Applying these considerations to a round radial flow heat exchanger, the device of the present invention provides greater fin surface area near the outer perimeter of the exchanger. This is important since the fluid enters on the outer perimeter and this is when the fluid has the most heat (or ability to absorb heat), as it has just arrived from the component that is being cooled (or heated). In short, there is greater surface area where there is greater heat to be exchanged.
The convective heat transfer coefficient h is a function of several variables. Some of these variables are (1) air temperature, (2) air humidity, (3) velocity of air flow over the fins, (4) volume of air over the fins, and (5) whether the air flow is laminar or turbulent around the fins. From a design standpoint, the three easiest variables to affect to increase heat exchange are (3), (4) and (5). Point number (5) will be touched on later, but for now (3) and (4) will be addressed.
If one is using forced convection to cool the exchanger, the velocity profile of the air out of a standard tube-axial fan is good for optimizing heat transfer with a round radial flow heat exchanger. Note that the highest velocity and volume of air is at the outer perimeter of the fan and decreases towards the center of the fan. This is important because this correlates also to the fin surface area profile of the heat exchanger. Stated another way, the highest air velocity and volume of air from a particular fan (biggest h) is being blown over the area of the heat exchanger with the highest fin surface area (biggest A), at the time that the fluid in the spokes has the most heat (Q) to exchange. This results in very efficient heat transfer.
As the fluid moves radially inward it loses more and more heat (ability to absorb heat decreases). At the same time, the fins on a radial flow heat exchanger get shorter and the airflow from the fan becomes less. To efficiently remove heat from the fluid as it moves radially towards the hub, less and less fin area and air flow are needed. Since these are inherent physical characteristics of a round radial flow heat exchanger and fan combination, heat transfer is optimized. In other words, it is more efficient from a materials usage perspective to have fins that get shorter and shorter. This optimized heat transfer implies another advantage.
(3) Lower Costxe2x80x94There are several details of this invention that will result in a lower cost heat exchanger when compared to a traditional rectangular machine-folded-fin heat exchanger.
(a) Efficient use of materialxe2x80x94As explained above, the efficient utilization of heat exchange material implies the need to use less of it. This leads to a lower raw material cost.
(b) No machine-folded-finsxe2x80x94As will be described in more detail later, this heat exchanger concept does not require the use of machine-folded-fins. The machines needed to make folded-fins are typically very expensive and produce fin stock at a slow rate. High capital investment and a slow production rate drive the final product cost up.
(c) Assembly processxe2x80x94The rate at which these exchangers can be assembled is fast. Additionally, the machines needed to produce final parts should be inexpensive. In large quantity production situations, if something can be produced faster, it is usually cheaper.
The radial flow heat exchanger of this invention may be used as coolant radiators in motor vehicles such as motorcycles, cars, trucks or other forms of transportation or as an oil cooler, either as original equipment or after-market installation. Other uses involve use as a heat exchanger in electronic devices (microchip cooling and the like), HVAC systems, air pre-filters, gas coolers, heat recovery systems, gas/gas re-heaters, and the like.
This invention has many other advantages, and other objectives, which may be more clearly apparent from consideration of the various forms in which it may be embodied. Certain versions of such forms are shown in the drawings accompanying and forming a part of the present specification. These forms will now be described in detail for the purpose of illustrating the general principles of the invention; but it is understood that such detailed description is not to be taken in a limiting sense.